In-Operando Spectroscopy to Study the Effect of Alkaloids on Polysulfide Shuttling in Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries are a promising next generation battery chemistry, but they are still hindered by the critical challenge of polysulfide shuttling. To address this problem, we investigated the novel application of alkaloids in lithium-sulfur batteries via in-operando IR spectroscopy. We did this by assembling an airtight electrochemical cell on top of an ATR-IR puck. To demonstrate the feasibility of the alkaloid material, we incorporated it into a sulfur cathode and studied the IR spectra in real time during battery cycling. We monitored the carbonyl peaks and found a reversible shift (strengthening/weakening) consistent with the appearance of polysulfides in the S-S region. This phenomenon corresponded directly with the 2.3V peak of the CV. This suggests a rapid polysulfide binding effect, as the polysulfides evolve, via polar-polar interactions between the oxygen of the carbonyl groups and lithium of the polysulfides. We believe the shift is particularly significant due to the presence of multiple carbonyl groups per molecule. This result is supported by shuttle current tests where we observed a lower concentration of polysulfides in the electrolyte for cells with the alkaloid material. We also incorporated this material into a conventional carbon-sulfur slurry cathode and saw an increase in both capacity and capacity retention. Finally, alkaloids can be derived from natural materials and represent a greener approach to the realization of the lithium-sulfur chemistry.